Question

Without referring to the chapter, draw the chair conformation of

(a) α -D-mannopyranose (the C2 epimer of glucose).

(b) β -D-allopyranose (the C3 epimer of glucose.)

(c) α -D-galactopyranose (the C4 epimer of glucose).

(d) N-formylglucosamine, glucose with C2 oxygen atom replaced by a formylated amino group.

Short answer

(a) α -D-mannopyranose (the C2 epimer of glucose).

(b) β -D-allopyranose (the C3 epimer of glucose.)

(c) α -D-galactopyranose (the C4 epimer of glucose).

(d) N-formylglucosamine, glucose with C2 oxygen atom replaced by a formylated amino group.

Step-by-step solution

A concept:

Pyranose is a six membered cyclic hemiacetal. For example, a six membered ring of glucose is known as glucopyranose. Sugars which have the common configuration like the arrangement of -H and -OH around carbon atoms are same except the carbon present at position or carbon number are known as epimers. For example, glucose and mannose are epimers of each other.

(a) α -D-mannopyranose (the C2 epimer of glucose).

A six membered ring of mannose is known as α -D-mannopyranose. The chair conformation of is shown by the figure below.

(b) β -D-allopyranose (the C3 epimer of glucose.)

A six membered ring of allose is known as β -D-allopyranose. The chair conformation of is shown by the figure below.

(c) α -D-galactopyranose (the C4 epimer of glucose).

A six membered ring of galactose is known as α -D-galactopyranose. The chair conformation of is shown by the figure below.

(d) N-formylglucosamine, glucose with C2 oxygen atom replaced by a formylated amino group.

When the C2 oxygen atom of glucose is replaced by a formylated amino group, it forms N-formylglucosamine. The chair conformation of N-formylglucosamine. is shown by the figure below.